In gas turbine engines, one or more shafts of the engine are usually subject to axial thrust loads during operation. Thrust loads arise in a gas turbine engine as a result of pressure imbalances. For example, a compressor has a higher downstream pressure than upstream pressure which forces the compressor upstream (towards the intake) whereas a turbine has a higher upstream pressure than downstream pressure which forces the turbine downstream (towards the exhaust nozzle). The thrust loads urging the compressor upstream and the turbine downstream may be high and uncertain.
The thrust loads are often at their maximum during the periods of highest power output for the engine. In a gas turbine engine providing jet propulsion for an aircraft, this period of maximized power output may occur when the aircraft is taking-off and/or climbing to a cruising altitude. The thrust loads may change direction (passing through a zero load point) during a flight cycle.
A thrust bearing may be positioned to support the shaft against these thrust loads. A thrust bearing typically comprises an inner race, an outer race, a cage, and a set of roller elements, the roller elements being spheres (or balls) which are contained within a raceway formed in one or both of the races with the cage maintaining the spacing between the balls.